ABSTRACT: Gel-like fat mixtures of high-melting (HM) andlow-melting (LM) fats were formed by means of rapid coolingand subsequent heating. No “non-fat” ingredients such as emul-sifiers, water, or waxes were added to the mixtures. The gel-likefats having solid fat content (SFC) values below 2.0 wt% formedcrystal networks of HM-fats that entrapped the liquid oil frac-tion of LM-fats. In a search for optimal fat combinations exhibit-ing gel-like behavior, fully hydrogenated rapeseed oil with ahigh amount of behenic acid (FHR-B), fully hydrogenated rape-seed oil with a high amount of stearic acid (FHR-S), tristearoyl-glycerol (SSS), triarachidonoyl-glycerol (AAA), and tribehenoyl-glycerol (BBB) were examined as the HM-fats. For LM-fats, salfat olein (SFO), cocoa butter (CB), palm super olein (PSO), andolive oil were examined. The following results were obtained:(i) the gel-like behavior was observed in mixtures of FHR-B/SFOand FHR-B/CB with initial concentrations of FHR-B of 1.5–4.0wt%. (ii) Rapid cooling to Tc (crystallization temperature) from70°C and subsequent heating to Tf (final temperature) were nec-essary to reveal the gel-like behavior, whereas simple coolingwithout a cooling/heating procedure did not form the gel-likefat mixture. (iii) Optimal values of Tc and Tf were related to them.p. of the LM-fat and HM-fat, respectively. (iv) Temperaturevariations of SFC as well as X-ray diffraction spectra showed thatthe melt-mediated transformation from α to β of the HM-fatcrystals was a prerequisite to reveal the gel-like behavior. Con-sequently, the fat mixture revealing the gel-like behavior mightbe called β-fat gel.

Paper no. J10361 in JAOCS 80, 263–270 (March 2003).

KEY WORDS: Cocoa butter, fully hydrogenated rapeseed oil,gel-like fat, polymorphism, sal fat olein.

Fats and oils are, in general, employed in industrial applica-tions in solid (crystalline), semisolid, emulsion (oil-in-waterand water-in-oil), gel, and liquid states. A gel state is definedas a two-phase colloidal system consisting of a solid and aliquid in a more solid form than sol, although there are vari-ous definitions representing the complicated nature of gelstates (1). Because of their smooth texture, viscoelasticity, ap-pearance, easy handling, and comfortable mouthfeel, gel ma-terials have attracted much attention in food, cosmetic, andpharmaceutical sciences and technology (2–5). Therefore, awide variety of research into gel phases made of polysaccha-

rides, proteins, and other biopolymer materials has been per-formed (6,7).

In a gel phase made of lipid emulsifiers and water, a lamel-lar-type lyotropic liquid crystal (LC) phase is formed at ele-vated temperatures. In the LC phase, a water phase is swelledinto a continuous lamellar LC phase. When this LC phase iscooled to undergo the transformation from the LC phase to acrystallization phase, the lamellar structure involving theswollen water phase is maintained, forming a highly viscousphase called an α-gel phase (8–10). Further cooling forms arheologically hard phase called a coagel. These gel phases areemployed as low-fat table spreads (11,12).

A gel phase containing oils and fats without lipid emulsi-fiers and water was formed by hydroxystearic acid, the hy-drogen bonding of which played the role of solidus networkto entrap the liquid oil phase (13,14). These gel fat materialshave been applied to nonedible uses. As for edible fats, cer-tain types of shortening containing high-melting (HM) fatsand liquidus oil exhibit gel-like behavior in the presence ofemulsifiers (15). It is known that peanut butter is formed bygel-like fats made of HM-fat fractions. However, the forma-tion mechanisms and physical properties of edible gel fatshave not been clarified in detail.

The aim of this work was to identify optimal combinationsof HM-fat and low-melting (LM) fat mixtures that exhibitgel-like behavior and to clarify the formation mechanism ofthe gel-like fat. No other ingredients such as emulsifiers,water, or waxes were included in the mixtures. Throughoutthis study, we set the highest concentration of HM-fat as 4.0wt%. The reason is that the presence of large amounts of HM-fats often results in a discontinuous texture of the fat blendmixture, which causes granular crystal formation and a sandymouthfeel. These properties are not favored for food usessuch as confections and creams.

In the present work, five kinds of HM-fats and four kinds ofLM-fats were examined, and various HM-fat and LM-fat mix-tures were subjected to different modes of cooling and heatingtreatment (tempering). Unique combinations of the HM- andLM-fats were found to form gel-like fats when the liquid mix-ture was rapidly cooled from a high temperature and a subse-quent heating procedure was applied. Solid fat content (SFC)and X-ray diffraction (XRD) analyses showed that the trans-formation from the α to the β form of the HM-fat fraction wasa prerequisite for the formation of gel-like fat mixtures.

Copyright © 2003 by AOCS Press 263 JAOCS, Vol. 80, no. 3 (2003)

*To whom correspondence should be addressed.E-mail: kyosato@hiroshima-u.ac.jp

Physical Analyses of Gel-like Behavior of Binary Mixturesof High- and Low-Melting Fats

K. Higakia, Y. Sasakuraa, T. Koyanoa, I. Hachiyaa, and K. Satob,*aConfectionery R&D Laboratory, Meiji Seika Kaisha Ltd., Saitama, 350-0289, Japan,

and bFaculty of Biological Science, Hiroshima University, 739-8528, Japan

MATERIALS AND METHODS

TAG components, FA components, and melting points (Tm)of fully hydrogenated rapeseed oil with a high amount of be-henic acid (FHR-B), fully hydrogenated rapeseed oil with ahigh amount of stearic acid (FHR-S), sal fat olein (SFO),palm super olein (PSO), olive oil, and cocoa butter (CB) areshown in Table 1. Multiple DSC melting peaks were observedfor LM-fats since various TAG with high and low Tm are con-tained. The Tm shown in Table 1 correspond to those of themajor fat components with highest DSC melting peaks.Minor HM-components are also present in the LM-fats. Forexample, SFO contains a few percent of the HM-fraction thatmakes a contribution to the SFC values of the mixtures. Tri-stearoyl-glycerol (SSS) (Tm = 73.1°C), triarachidonoyl-glyc-erol (AAA) (Tm = 78.0°C), and tribehenoyl-glycerol (BBB)(Tm = 82.5°C), each having a purity of >99%, were purchasedfrom Tokyo Kasei Co., Tokyo, Japan.

After weighing the component fats, the HM- and LM-fatswere mixed at 70°C and then subjected to a tempering process.Three factors of the tempering process were varied to search forthe optimal thermal treatments producing the gel-like behavior:(i) Cooling rate (Vc) is the rate of cooling from 70°C to crystal-lization temperature (Tc); 10 and 1.5°C/min were examined astypical Vc values. (ii) Tc determines the polymorphic forms ofthe first crystallized structure of the HM-fats. The Tc values ex-amined were 20, 25, 30, 35, and 38°C. The crystallized sampleswere held at Tc for 10 min and then subjected to heating at a rateof 2°C/min. (iii) Heating to Tf (final temperature) and isother-

mal treatment at Tf caused melting of the crystal form that wascrystallized at Tc and transformation to more stable forms. TheTf values examined were 30, 35, 38, 41, 43, and 45°C.

Gel-like behavior was observed visually by putting the fatmixtures in test tubes and tilting them 45° from vertical. Gel-like behavior was identified when no deformation occurredand liquid and solid phases did not separate.

A rotator-anode (RA) XRD spectrometer using a RINT-TTR (Rigaku, Tokyo) (8.4 kW; 42 kV; 200 mA) was em-ployed to determine the polymorphic forms of the crystallizedHM-fats, with a vertical goniometer and an RA of Cu-Kα(wavelength, 0.154 nm) radiation with Ni filter. The moltensample (ca. 0.5 g) was mounted on the XRD aluminum platein a horizontal arrangement, and the sample temperature wasdecreased in a temperature-controlled sample holder.

SFC values were measured by pulsed NMR (PC120;Bruker, Karlsruhe, Germany). Sample (1.5 g) was placed in aglass cell (diameter: 7 mm), in which a tempering process wasperformed by using the temperature-control system of theNMR equipment.

RESULTS

Visual observation. This section describes the results of vi-sual evaluation of fluidity of various fat mixtures that weresubjected to the tempering procedures with different valuesof Vc, Tc, and Tf .

In Figure 1 one can see the gel-like behavior of the FHR-B(2.0 wt%)/SFO fat mixture that was subjected to three ther-

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TABLE 1Melting Points, FA Compositions, and Carbon Number of TAG in High-Melting Fats and Low-Melting Fatsa

High-melting fats Low-melting fats

Melting point FHR-B FHR-S SFO PSO Olive oil CB(°C) 65.8 68 12 7.0 5.0 34

FA composition12:0 — — — 0.3 13.1 —14:0 0.1 — 0.1 1.0 0.5 —16:0 3.2 4.9 8.5 32.0 — 24.416:1 — — — 0.4 — —18:0 37.3 91.3 24.2 3.0 2.1 35.418:1 0.2 — 56.0 49.0 79.3 38.118:2 — — 3.9 13.5 4.7 2.118:3 — — 0.7 0.8 0.2 —20:0 9.8 2.5 4.9 — 0.1 —22:0 47.8 1.3 0.4 — — —24:0 1.6 — — — — —

Carbon number48 — — 0.2 2.1 — 1.250 0.7 4.2 3.4 24.0 4.8 17.052 3.5 17.5 14.0 58.5 29.8 44.054 8.3 67.5 51.8 14.9 65.4 34.856 9.4 4.7 10.0 0.5 — —58 15.4 — — — — —60 19.4 — — — — —62 39.6 — — — — —

aFHR-B, fully hydrogenated rapeseed oil with a high amount of behenic acid; FHR-S, fully hydro-genated rapeseed oil with a high amount of stearic acid; SFO, sal fat olein; PSO, palm super olein;CB, cocoa butter.

mal treatments with Tc = 20°C and Tf = 38°C. When the mix-ture was directly cooled from 70 to 38°C (no tempering), asol-like fat mixture was formed (Fig. 1A). The tempered fatsthat were cooled to Tc = 20°C with Vc = 1.5°C/min and heatedto Tf =38°C also showed sol-like behavior (Fig. 1B). In con-trast, gel-like behavior was exhibited when the fat mixturewas tempered a Vc =10°C/min as shown in Figure 1C underthe same conditions as in Figure 2B. The same results were

observed for the other fat mixtures that exhibited gel-like be-havior (see below). Therefore, the Vc value was maintained at10°C/min during all the experiments that followed.

Table 2 shows the results of visual evaluation of the fatmixtures of FHR-B/SFO at different concentrations ofFHR-B when Tc was varied from 20 to 38°C, and the tem-pered fats were kept at Tf = 38°C for 60 min. At all Tc valuesexamined, sol-like mixtures were formed when concentra-tions of FHR-B did not exceed 1.5 wt%. At the 1.5 wt% con-centration of FHR-B, gel-like behavior was observed at Tc =20°C, whereas the mixture became sol-like when Tc increasedabove 20°C. At FHR-B concentrations of 2.0 and 4.0 wt%,the mixtures became gel-like below Tc = 25°C (FHR-B: 2.0wt%) and below Tc = 30°C (FHR-B: 4.0 wt%). This resultshows the importance of the crystallization of the α form ofFHR-B in the FHR-B/SFO liquid mixture at Tc = 20–25°C bychilling from 70°C at a rate of 10°C/min at the concentrationsof FHR-B above 2.0 wt%. The α crystals of FHR-B thusformed are converted to β crystals through α-melt mediationafter subsequent rapid heating, as shown below.

Table 3 shows the results of visual evaluation of fluiditybehavior of the fat mixtures of FHR-B/SFO kept at different

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FIG. 1. Optical photographs showing sol-like and gel-like behavior of a fat mixture of FHR-B (2.0 wt%)/SFO. Tc =20°C, Tf = 38°C. A (70°C → Tf ); B (70°C → Tc → Tf , Vc = 1.5°C/min); C (70°C → Tc → Tf , Vc = 10°C/min). FHR-B, fully hydrogenated rapeseed oil with a high amount of behenicacid; SFO, sal fat olein; Tc, crystallization temperature; Tf, final temperature.

FIG. 2. (A) Difference in solid fat content (SFC) values of FHR-B (2.0wt%)/SFO mixture. Tc = 20°C, Tf = 38°C for 60 min. (B) SFC values ofthe different low-melting fats with FHR-B (2.0 wt%) during the temper-ing process. 20°C → 38°C (60 min) → 60°C, Vc = 10°C/min). For ab-breviations see Figure 1.

TABLE 2Effects of Tc on Gel-like Behavior of FHR-B/SFO Mixtures at Vc = 10°C/min and Tf = 38°C (for 60 min)

Concentration Concentration Tc (°C)a

of FHR-B (wt%) of SFO (wt%) 20 25 30 35 38

0 100 — — — — —0.5 99.5 — — — — —1.0 99.0 — — — — —1.5 98.5 ▲▲ — — — —2.0 98.0 ●● ●● — — —3.0 97.0 ●● ●● ▲▲ — —4.0 96.0 ●● ●● ●● — —a●●: gel-like, ▲▲: somewhat gel-like, —: liquidus. Tc: crystallization tempera-ture; Tf : final temperature; Vc: cooling rate; for other abbreviations seeTable 1.

Tf values for 60 min, after crystallization at Tc = 20°C with Vc = 10°C/min. Gel-like behavior was noted with in-creasing amounts of FHR-B at all Tf values, whereas the solmixture was formed at Tf above 41°C at FHR-B concentra-tions of 1.5 and 2.0 wt%. As for FHR-B concentrations of 3.0and 4.0 wt%, gel-like behavior was revealed by the fluidityevaluation. However, the formation behavior was quite dif-ferent between the Tf values below and above 38°C, as shownby the SFC measurement (see next section).

Table 4 summarizes the occurrence of the gel-like behav-ior of various combinations of the HM- and LM-fats at con-centrations of 2.0 and 98.0 wt%, respectively. The temperingconditions were as follows: Vc = 10°C/min, Tc = 20°C, and Tf= 38°C (60 min). The two LM-fats, PSO, and olive oil did notshow gel-like behavior with the five HM-fats, probably be-cause α crystals were not formed in the mixtures using PSOand olive oil.

Similarly, FHR-S, SSS, AAA, and BBB did not demon-strate gel-like behavior with the four LM-fats. As for the mix-tures of AAA/SFO, AAA/CB, BBB/SFO, and BBB/CB,solidus mixtures were formed at 38°C, yet slight separationof fats and liquids occurred after 60 min, meaning that thosemixtures did not form gel-like fats.

Isothermal treatment at T = Tf. The visual observations de-scribed in the previous section reflected the fact that the tem-pering process, with rapid cooling of the liquid mixture andsubsequent heating, was necessary to reveal the gel-like be-havior. To analyze these properties in situ, SFC values were

measured during the isothermal treatment of the fat mixture ofFHR-B (2.0 wt%)/SFO at Tf = 38°C after cooling to Tc = 20°Cat Vc = 10°C/min and Vc = 1.5°C/min. In addition, visual ob-servation was also made during the isothermal treatment.

Figure 2A shows the SFC values of a FHR-B (2.0wt%)/SFO mixture at Vc of 10 and 1.5°C/min during isother-mal treatment at Tf = 38°C for 60 min. The SFC value wasabout 3.0% before the temperature changed from 20°C. Thisvalue increased to more than the initial concentration of theHM-fat in the mixture owing to crystallization of the HM-fraction in SFO at 20°C. At about 6 min after the isothermaltreatment started, the SFC value fell to 1.2% and did notchange within 60 min. By contrast, the SFC value of the fatmixture that was cooled at Vc = 10°C/min to 20°C decreasedto 0% at 8 min after the isothermal treatment started. The SFCvalue then gradually increased to 1.4% at around 30 min. Thisresult showed that the crystals, which were formed by rapidcooling to 20°C in the FHR-B/SFO mixture, completelymelted at Tf = 38°C, and recrystallization occurred during theisothermal treatment. Therefore, melt-mediated transforma-tions occurred during the heating from 20 to 38°C andisothermal treatment at 38°C.

Figure 2B shows the time variation of the SFC values ofthe four fat mixtures, in which the HM-fat was FHR-B (2.0wt%) and the LM-fats (98.0 wt%) were SFO, PSO, olive oil,and CB. These fat mixtures were subjected to a temperingprocess of Vc = 10°C/min, Tc = 20°C, and Tf = 38°C. Duringheating from 20 to 38°C, the SFC values of the mixtures ofFHR-B/SFO and FHR-B/CB decreased to 0% and thereafterincreased to 1.4%, whereas the other two mixtures did notshow this conversion. Figure 2B also shows that the four fatmixtures melted when the temperature was raised above38°C, indicating that the HM-fraction crystals melted and thegel-like property disappeared.

Figure 3 shows the effects of the duration of isothermaltreatment at Tf = 38°C on the conversion from sol-like to gel-like behavior of FHR-B (2.0 wt%)/SFO that was temperedwith Vc = 10°C/min and Tc = 20°C. Ten minutes after Tf wasreached (Fig. 3A), the fat mixture was sol-like. However, thegel-like property was observed as the duration of the isother-mal treatment was extended, and a completely gel-like fat wasformed at 40 min (Fig. 3D). This result showed good agree-ment with those shown in Figures 2A and 2B.

Figure 4 shows in situ RA-XRD experiments in which afat mixture of FHR-B (4.0 wt%)/SFO was subjected to thetempering procedures of Tc = 20°C, Tf = 38°C at (A) Vc = 10and (B) 1.5°C/min. The peaks in the XRD spectra were broadsince the concentration of the fat crystal was low and liquidcontent was high. However, it was confirmed that the α formwas crystallized at 20°C when the mixture was cooled at Vc =10°C/min, as revealed in a long-spacing spectrum of 1.96 nm(003 reflection) and a short-spacing spectrum of 0.41 nm (16)as shown by arrows in Figure 4A. After heating to 38°C, theXRD peaks of the α form disappeared and those of the βform, having a long-spacing spectrum of 1.73 nm (003 reflec-tion) and a short-spacing spectrum of 0.46 nm, appeared (16).

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TABLE 3Effects of Tf on Gel-like Behavior of FHR-B/SFO Mixtures at Vc = 10°C/min and Tc = 20°C

Concentration Concentration Tf (°C)a

of FHR-B (wt%) of SFO (wt%) 30 35 38 41 43 45

0 100 — — — — — —0.5 99.5 — — — — — —1.0 99.0 — — — — — —1.5 98.5 ●● ●● ▲▲ — — —2.0 98.0 ●● ●● ●● — — —3.0 97.0 ●● ●● ●● ●● ●● —4.0 96.0 ●● ●● ●● ●● ●● ●●

aThe mixtures were held at each Tf for 60 min. For abbreviations seeTables 1 and 2; for symbols see Table 2.

TABLE 4Evaluation of Occurrence of Gel-like Behaviora of the Fat Mixtures of Different Combinations of High-Melting Fats (2.0 wt%) and Low-Melting Fats (98.0 wt%)

Low-melting fat

High-melting fat SFO PSO Olive oil CB

FHR-B ●● — — ●●

FHR-S — — — —SSS — — — —AAA — — — —BBB — — — —aSSS: tristearoyl-glycerol; AAA: triarachidonoyl-glycerol; BBB: tribehenoyl-glycerol; for other abbreviations see Table 1. For symbols see Table 2.

By contrast, the β′ and β forms were formed at 20°C whenthe liquid fat mixture was cooled to 20°C at Vc =1.5°C/min(Fig. 4B), and the β′ form transformed to the β form duringthe process of heating to 38°C.

From these results, it can be concluded that the melt-medi-ated transformation of the fat mixture of FHR-B/SFO duringisothermal treatment after tempering of Vc =10°C/min and Tc =20°C was due to the melt-mediated transformation from the αform to the β form of FHR-B crystal fractions in the mixtures.

DISCUSSION

The visual evaluation, SFC, and X-ray diffraction analyses ofvarious binary mixtures of HM- and LM-fats can be summa-rized as follows: (i) Two combinations of FHR-B/SFO andFHR-B/CB exhibited gel-like behavior in a temperature rangeabove the Tm of the LM-fat and below the Tm of the HM-fatfraction in the mixture phase. The other combinations did notshow the gel-like behavior. (ii) Simple cooling of these twomixtures, from high-temperature liquidus mixture to Tf , didnot result in formation of the gel-like fat. Instead, a propertempering process was a prerequisite. This tempering processinvolved rapid cooling to Tc, to induce the crystallization ofthe HM-fat, and subsequent heating to Tf , to induce the melt-ing of the first-crystallized form and crystallization of themore stable form. (iii) The process of heating from Tc to Tfcaused melt-mediated transformations in which the α form,which was crystallized by rapid cooling to Tc, completelymelted and the most stable β form was crystallized. As theisothermal crystallization of the β form proceeded at Tf , thegel-like behavior was intensified and was completed after 40min. (iv) Consequently, the fat mixture exhibiting the gel-likebehavior might be called β-fat gel, in a comparative mannerto the previously reported α-gel (8–10).

To understand these results, we propose a mechanisticmodel for the formation of the β-fat gel mixture containing theHM (1.5–4.0 wt%)- and LM (96–98.5 wt%)-fats, as shown inScheme 1. Two key mechanisms are prerequisites in thismodel (where HMF = high-melting fat and LMF = low-melt-ing fat): (i) The α-form crystals of the HM-fat formed in thecooling process at Tc are randomly distributed in a liquid phaseof the LM-fat; (ii) the α-melt-mediated transformation pro-vides heterogeneous nucleation sites for the β crystals, whichform a network of randomly distributed crystals through themelt-mediated transformation from the α crystals. In the pres-ent heating treatment from Tc to Tf , it is reasonable to assumethat solid-state transformation from α to β was not a dominat-ing process, as judged from the variation of the SFC valueswith time–temperature (Fig. 2.) The proposed model may ex-plain our experimental results as follows.

The fact that Vc must be large, e.g., 10°C/min, is related tothe formation of the α crystals, which are prerequisites for gelformation. In general, β form crystals are usually crystallizedfrom solution; α and β′ forms are rarely crystallized from so-lution (17). To interpret this observation, it is assumed thathigh diffusion rates of molecules in solution may cause thecrystallization of the β form, which has the most denselypacked subcell structure; the less stable α or β′ forms, withless densely packed subcell structures, are not formed fromsolution phase (18). If a highly supercooled condition occurs

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FIG. 3. Time variation of the liquidus to gel-like fat mixtures of FHR-B(2.0 wt%)/SFO during isothermal treatment at Tf = 38°C, after temper-ing with Vc = 10°C/min, Tc = 20°C. (A) 10 min, (B) 20 min, (C) 30 min,and (D) 40 min. For abbreviations see Figure 1.

FIG. 4. X-ray diffraction spectra of fat mixture of SFO/FHR-B (4.0 wt%)during tempering. (A) Vc = 10°C/min; (B) Vc = 1.5°C/min. Units: nm.For abbreviations see Figure 1.

during the crystallization from solution phase, the α or β′forms may be crystallized. In this regard, the α form was re-cently reported to crystallize from mixtures of fats and oils,as the viscosity of the oil phase is increased and the rate ofcrystallization is increased (19). This phenomenon may haveoccurred in the present case, although further examination isneeded to confirm this consideration. The facts that slow cool-ing to Tc did not lead to the formation of the α form (Scheme1) and that subsequent heating did not reveal gel-like behav-ior may be explained by this mechanism. It is assumed thatthe LM-fats of SFO and CB may satisfy the condition to crys-tallize the α form, whereas the other LM-fats may be too fluid(i.e., unviscous) (or too low-melting) to permit crystallizationof the α form of the HM-fat fraction even at a high Vc value.

The products of the melt-mediated α → β transformationof the HM-fat at Tf form the sites of further rapid growth of the β crystals. It has been reported that the α-melt media-tion induces the crystallization of the more stable β′ and β forms much faster than the simple cooling from liquid,as quantitatively measured for PPP (tripalmitoyl-glycerol)

(19), SOS (1,3-stearoyl-2-oleoyl glycerol) (21–23), POP (1,3-palmitoyl-2-oleoyl glycerol) (20), and POS (24). Inparticular, in situ synchrotron radiation XRD analysis ofthe α-melt-mediated transformations of SOS showed that

highly accelerated nucleation was induced by α-melt media-tion (22).

The β crystals of the HM-fats might be nucleated at thevery sites of the α crystals that melted during heating from Tcto Tf . Since the nucleation rates of the β form are so high bythe α-melt mediation that the number of the β crystals is largecompared with that formed by simple cooling. In addition, theα crystals are distributed randomly in the liquid phase of theLM-fat, and thereby the heterogeneous nucleation sites of βcrystals are also randomly distributed. Thus, the sizes of theβ crystals are so small and the nucleation sites of the β crys-tals are so randomly distributed that randomly distributed tinyβ crystals may form a crystal network that incorporates the

liquid phase of the LM-fat as depicted in Scheme 1. By con-trast, the β crystals formed by simple cooling to Tf or by tem-pering with Vc < 1.5°C/min are too small in number and toolarge in size to form the gel-like fat mixture. These β crystalsmight be precipitated and aggregated so that liquid and solidfractions are separated to form the sol phase as shown inScheme 1.

To verify this, optical images of the β crystals of FHR-B(2 wt%) in the FHR-B/SFO (98 wt%) mixtures formed at Tf = 38°C are shown in Figure 5. Figures 5A and 5B show βcrystals with tempering at Vc = 1.5 and 10°C/min, respec-tively. The former crystals are large in size and nonuniformlydistributed, but small crystals are uniformly distributed in thelatter case.

In this regard, the morphology of the β form may also beimportant. The fact that FHR-B exhibited gel-like behavior,whereas the other HM-fats did not, must mean that the Tm isnot the major cause for the formation of gel-like fat mixture.The Tm of the β forms of the HM-fats examined in this workare 65.8°C (FHR-B), 68.0°C (FHR-S), 73.5°C (SSS), 78.1°C(AAA), and 82.5°C (BBB); FHR-B, with the lowest Tm, ex-hibited gel-like behavior. Alternatively, morphology and net-work formation of the β form of the high-melting fat must behighly influential. It is known that needle-like morphology istypical for the β form (25). This morphology is evident in theβ forms of the five HM-fats examined. However, it is alsopossible to infer that specific needle morphology, such asthinness and sharpness, and network formation of β crystalsof FHR-B might be most suitable to incorporate the liquidfraction of the LM oils, compared to those of FHR-S, SSS,AAA, and BBB.

Although not shown here, the five HM-fats exhibited theα-melt-mediated transformation into the β form in SFO dur-ing the temperature processes. This means that randomnessin the β crystal distribution may also be significant, probablyas it relates to fractal analyses (26–28) in addition to morpho-logical influence.

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SCHEME 1

ACKNOWLEDGMENTS

The authors are deeply indebted to Dr. Satoru Ueno and MorioTakeuchi, Graduate School of Biosphere Science, Hiroshima Uni-versity, for their kind assistance in RA-XRD measurements andvaluable discussion.

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FIG. 5. Optical micrographs of fat mixtures of SFO (98.0 wt%)/FHR-B(2.0 wt%) crystallized with two Vc values. For abbreviations see Fig-ure 1.

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[Received June 21, 2002; accepted November 25, 2002]

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